Multi-sensor signal fusion for modulation classification of weak signals

ABSTRACT

A multi-sensor signal fusion apparatus is provided for automatic modulation classification of weak unknown signals in non-cooperative communication environment with a more accurate description of the signal. The multi-sensor non-cooperative demodulation device combines a group of sensors, a signal fusion sensor, a means for signal demodulation, and a means for automatic modulation classification. An output of the signal fusion sensor is sent to a means for modulation scheme classification to select the appropriate demodulation technique for demodulating the unknown signal and provide the necessary intelligence about the monitored signals to the user and allow the user to simulate the unknown non-cooperative signal. The present invention also contemplates a multi-sensor signal fusion article of manufacture with a storage medium encoded with machine-readable computer program code for more accurate descriptions of monitored signals and methods for achieving higher accuracy descriptions of monitored signals in a non-cooperative environment with multi-sensor non-cooperative demodulation.

GOVERNMENT INTEREST

The invention described herein may be manufactured, used, imported,sold, and licensed by or for the Government of the United States ofAmerica without the payment to me of any royalty thereon.

FIELD OF THE INVENTION

The invention generally relates to signal collection networks. Inparticular, the invention relates to signal monitoring apparatus andmethods based on multi-sensor fusion for modulation classification ofweak signals.

BACKGROUND OF THE INVENTION

Non-cooperative demodulation is a technique to demodulate communicationsignals without hand shaking between the transmitter and the receiver.This technique has been widely used in both military and commercialcommunications, battlefield surveillance, hostile signal detection, andsignal monitoring. In non-cooperative communications, the receiver hasno knowledge, or only has limited knowledge of the transmitting signal,for example the signal monitoring devices may not know the format of thesignal being monitored in tactical or hostile environment involvingmilitary or law enforcement operations. Non-cooperative demodulationwill be used in non-cooperative communication.

Automatic modulation classification is a key component innon-cooperative demodulation for recognizing the modulation scheme of atransmitted signal without prior knowledge of the signal ground truthand cueing the software-defined radio to choose the proper built-indemodulator. Although significant research has been conducted onautomatic modulation classification methods during the last two decades,this research has been limited to single receiver situations where theclassification performance and recognition of a successful rate havelargely depended on channel quality and the receiver signal strength.These conditions do not ordinarily apply to non-cooperativecommunications because in a non-cooperative communication environment,particularly in military applications, the received signal at the singlesensor is usually very weak so that the single sensor modulationclassification of an unknown weak signal is usually difficult andunreliable.

Further, prior art automatic modulation classification devices andmethods do not adequately account for multiple receiver situations suchas sensor networks; whose uses have become more and more popular. Due tothe dramatic and widespread use of sensor networks, single sensormonitoring is now considered to be inadequate.

Thus, there has been a long-felt need for better signal monitoringtechniques that lead to more effective modulation classification of weaksignals without suffering from the limitations, shortcomings anddifficulties of single receiver configurations such as receiving weaksignals and classifying the unknown weak signal.

SUMMARY OF THE INVENTION

In order to meet the long-felt need for more effective signal monitoringand improved demodulation, without suffering from the limitations,shortcomings and difficulties of prior art configurations, thisinvention's multi-sensor signal fusion devices and methods combinesignals from multiple sensors to provide descriptions of the monitoredsignals that are more accurate than single signal demodulation.Multi-sensor signal fusion offers increased reliability and huge gainsin overall performance compared to the single-sensor demodulation sothat the automatic modulation classification of weak signals innon-cooperative communication environment could be stronger and morereliable. This invention's multi-sensor signal fusion devices also takeadvantage of the latest techniques for improving geo-location accuracyand eliminating the channel distortion of the transmitted signals.

Thus, it is an object of the present invention to provide a multi-sensorsignal fusion apparatus for automatic modulation classification of anunknown signal.

Another object of the present invention is to provide a multi-sensorsignal fusion apparatus for automatic modulation classification thatprovides a more accurate description of an unknown signal.

It is a further object of the present invention to provide amulti-sensor signal fusion apparatus for automatic modulationclassification of weak signals in a non-cooperative communicationenvironment that provides a more accurate description of an unknownsignal.

These and other objects and advantages can now be attained by thisinvention's multi-sensor non-cooperative demodulation device comprisinga group of sensors, a signal fusion sensor, a means for signaldemodulation, and a means for automatic modulation classification. Anoutput of the signal fusion sensor is sent to a means for modulationscheme classification to select the appropriate demodulation techniquefor demodulating the unknown signal to provide the necessaryintelligence about the monitored signals to the user. This invention'smulti-sensor non-cooperative demodulation device, system and methodsprovide more accurate descriptions of monitored signals in anon-cooperative environment without suffering from the disadvantages,shortcomings and limitations of prior art techniques and devices.

The present invention also contemplates a multi-sensor signal fusionarticle of manufacture with a storage medium encoded withmachine-readable computer program code for more accurate descriptions ofmonitored signals and methods for achieving higher accuracy descriptionsof monitored signals in a non-cooperative environment with multi-sensornon-cooperative demodulation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a typical communication sensor network;

FIG. 2 is a conceptual block diagram depicting a simplified version ofthe multi-sensor non-cooperative demodulation device in accordance withthe present invention;

FIG. 3 is a software programming flowchart depicting software operationsof non-cooperative demodulation in accordance with the presentinvention;

FIGS. 4A and 4B show a conceptual block diagram illustratingmulti-sensor signal fusion with master and slave sensors in accordancewith the present invention;

FIG. 5A is a chart illustrating the simulation result of a single sensorwith a matched filter;

FIG. 5B is a chart illustrating the simulation result of multi-sensorsignal fusion with a matched filter;

FIG. 6 is a chart illustrating the simulation result of multi-sensorsignal fusion without matched filters;

FIGS. 7A and 7B show a conceptual block diagram depicting automatedmodulation classification for linear communication signals in accordancewith the multi-sensor non-cooperative demodulation device of the presentinvention; and

FIG. 8 is a flowchart depicting the steps of the method for achievinghigher accuracy descriptions of monitored signals in a non-cooperativeenvironment with multi-sensor non-cooperative demodulation in accordancewith the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In accordance with the present invention, fusing multiple signals inconnection with non-cooperative demodulation affords a more effectivedemodulation without suffering from the limitations, shortcomings, anddifficulties of single receiver configurations, such as receiving weaksignals and classifying the unknown weak signal. FIG. 1 is a diagramillustrating a typical communication sensor network with an unknowntransmitter T and N number of communication sensors, denoted by R₁, R₂,. . . , and R_(N). The unknown transmitted signal is transmitted by atransmitter T and is collected by sensors R₁, R₂, . . . , and R_(N)non-cooperatively. In this diagram, the sensors can communicate witheach other cooperatively, but they do not need to be fully connected.The sensors have no hand-shaking with the unknown transmitter, T.

FIG. 2 is a conceptual block diagram depicting a simplified version ofthe multi-sensor non-cooperative demodulation device 10, comprising agroup of sensors, a signal fusion sensor, a means for signaldemodulation that generates a demodulated signal, and a means forautomatic modulation classification to estimate a modulation scheme.Referring now to FIG. 2, multiple sensors 11, 12, and N receivenon-cooperative signals, from an unknown transmission source. Thesensors 11, 12 and N, each have a sampling clock to digitize thereceived signals and a local memory to store the received signals,r_(0i), 13 in the form of signal packets. Denoting the unknown signal ass(t), the received signal, r_(0i), 13, at the i^(th) sensor is describedby the following expression:r _(0i)(t)=a _(0i)(t)s(t−τ _(i))+n _(0i)(t)+I _(0i)(t)  Equation (1)where a_(0i)(t) is the channel attenuation between the transmitter T andreceiver R_(i), n_(0i)(t) is the additive noise with a zero mean betweenthe transmitter T and receiver R_(i), and I_(0i)(t) is a combination ofrandom interferences between the transmitter T and receiver R_(i). Thereceived signals 13 are combined in a signal fusion sensor 14 thatextracts the weak signals and generates a combined, or fused, digitizedsignal 15. The received signal at the first sensor 11 digitizes a shorttime duration, or fragment, of the received signal r_(0i)(t) to Ksamples, which are time-stamped and stored in the local memory as apacket. Let t=kT_(s), in EQ. 1, the digitized signal at the firstreceiving sensor 11 can approximately be described by:r ₀₁(kT _(s))=a ₀₁(kT _(s))s((k−m ₁)T _(s)−δ₀₁)+n ₀₁(kT _(s))+I ₀₁(kT_(s))  Equation (2)where k=1, 2, . . . , K, T_(s) is the sampling time-period, m₀₁ is apositive integer contributed by the transmission time-delay, and δ₀₁ isa decimal number between −0.5T_(s) and 0.5T_(s) related to the reminderof τ_(i)/T_(s). The digitized received signals from all sensors, 11, 12,and N are combined at the signal fusion sensor 14 to form the combineddigitized signal 15 which is sent to a means for automatic modulationclassification 16 to estimate a modulation scheme that simulates themodulation of the unknown signals, s(t).

An output estimate 16A is sent to a means for modulation schemeclassification 17 that selects the appropriate demodulation techniquefor demodulating the unknown signals, s(t), such as PSK8, FSK2 andQAM16. The signal demodulation means 18 classifies the unknown signals,s(t), and provides a demodulated signal 19 with improved fidelity andreliability allowing the user to better conduct hostile signaldetection, surveillance, and monitoring.

This invention's multi-sensor demodulation device 10 eliminates signalvariables such as the power of the channel noise, disturbances andcombined interference by taking advantage of the spatial diversity andrandomness of those unknown terms and digitizing a fragment of thereceived signal r_(0i)(t) to K samples. The resolution of the combineddigitized signal 15 depends upon the sampling rate. Since the samplingclocks at the receiving sensors 11, 12 and N are asynchronous andjittering in a given time frame, the digitized receiving signalsr_(0i)(kT_(s)) have a small time offset referencing to the firstreceiving sensor 11. It is reasonable to assume the sampling time-periodT_(s) is fixed within the analysis time frame, the signal r_(0i)(kT_(s))can be described byr _(0i)(kT _(s) −d _(0i))=a _(0i)(kT _(s) −d _(0i))s((k−m _(i))T_(s)−δ_(0i))+n _(0i)(kT _(s) −d _(0i))+I _(0i)(kT _(s) −d_(0i))  Equation (3)where d_(0i) is the time-synchronization offset, δ_(0i) is a decimalnumber between −0.5T_(s) and 0.5T_(s), which is a remainder related totime-quantization, time-synchronization, and time-jittering. Since thecommunication between T and R_(i) is non-cooperative, the channelequalization and signal recovery at each single sensor is verydifficult.

For simplification, denotingr _(0i)(k)=r _(0i)(kT _(s) −d _(0i)),a _(0i)(k)=a _(0i)(kT _(s) −d_(0i)),n _(0i)(k)=n _(0i)(kT _(s) −d _(0i)), andI _(0i)(k)=I _(0i)(kT _(s) −d _(0i))and combining EQ. 2 and EQ. 3 results in the expression:r _(0i)(k)=a _(0i)(k)s(k−m _(i))T _(s)−δ_(0i))+n _(0i)(k)+I_(0i)(k)  Equation (4)where i=1, 2, . . . , N, and δ_(1,1)=0. In this simplified embodiment,the first receiving sensor, R₁, or 11, functions as a master and allother sensors: R₂, R₃, . . . , R_(N) (12 and N) function as slavespassing the received signal packets from the local memories to themaster in various relay routes for data fusion. The communicationsbetween the master and slaves can be wired or wireless.

The cooperation between the master and slaves is a critical element ofthe signal fusion aspect of the present invention. The signaltransmission from slaves to the master is asynchronous in time since alldata fragments are sent as packets. Furthermore, when the communicationsbetween sensors are cooperative, the channel distortion to the datatransmission can be compensated for and the data can be recoveredreliably by using various existing techniques such as error coding,interleaving, and equalization. The received packet at the mastercontains K signal samples, which are described by:

$\begin{matrix}{{r_{i}(k)} = {{{{a_{i\; 1}(k)}{r_{0\; i}(k)}} + {n_{i\; 1}(k)} + {I_{i\; 1}(k)}} = {{{a_{i}(k)}{s\left( {\left( {k - m_{i}} \right)T_{s}} \right)}} + {\Delta\;{s_{i}(k)}} + {n_{i}(k)} + {I_{i}(k)}}}} & {{Equation}\mspace{14mu}(5)}\end{matrix}$where k=1, 2, . . . , N, a_(i)(k)=a_(i1)(k)a_(0i)(k),n_(i)(k)=n_(0i)(kT_(s)−d_(0i))+n_(i1)(k),I_(i)(k)=I_(0i)(kT_(s)−d_(0i))+I_(i1)(k), n_(i1)(k) is the additivechannel noise between the i^(th) slave and the master with n_(1,1)(k)=0,and I_(i1)(k) represents the random combined disturbances between thei^(th) slave and the master with I_(1,1)(k)=0. The following termdescribes the signal distortion due to digitization:Δs _(i)(k)=a _(i1)(k)a _(0i)(k)s((k−m _(i))T _(s)−δ_(0i))−a_(i)(k)s((k−m _(i))T _(s))  Equation (6)After the master takes all packets from the memories of R₂, R₃, . . .R_(N), the signal samples are aligned and combined into a single signal.Various methods can be used in aligning and combining signals. One wayis to shift the waveform with an estimated delay of {circumflex over(m)}_(i), i=2, . . . , N, and {circumflex over (m)}₁=0, and calculatethe expectation of all shifted signals as described by these equations:

$\begin{matrix}{{y(k)} = {{{\frac{1}{N - 1}{\sum\limits_{i = 1}^{N}\;{r_{i}\left( {k + {\hat{m}}_{i}} \right)}}} \approx {{\left( {\frac{1}{N - 1}{\sum\limits_{i = 1}^{N}\;{a_{i}(k)}}} \right){s\left( {kT}_{s} \right)}} + {\frac{1}{N - 1}{\sum\limits_{i = 1}^{N}\;{\Delta\;{s_{i}\left( {k + {\hat{m}}_{i}} \right)}}}} + {\frac{1}{N - 1}{\sum\limits_{i = 1}^{N}\;{n_{i}\left( {k + {\hat{m}}_{i}} \right)}}} + {\frac{1}{N - 1}{\sum\limits_{i = 1}^{N}\;{I_{i}\left( {k + {\hat{m}}_{i}} \right)}}}}} = {{{A(k)}{s\left( {kT}_{s} \right)}} + {\Delta\;{S(k)}} + {L(k)} + {I(k)}}}} & {{Equation}\mspace{14mu}(7)}\end{matrix}$where

${{A(k)} = {\frac{1}{N - 1}{\sum\limits_{i = 1}^{N}\;{a_{i}(k)}}}},{{\Delta\;{S(k)}} = {\frac{1}{N - 1}{\sum\limits_{i = 1}^{N}\;{\Delta\;{s_{i}\left( {k + {\hat{m}}_{i}} \right)}}}}},{{L(k)} = {\frac{1}{N - 1}{\sum\limits_{i = 1}^{N}\;{n_{i}\left( {k + {\hat{m}}_{i}} \right)}}}},{{{and}\mspace{14mu}{I(k)}} = {\frac{1}{N - 1}{\sum\limits_{i = 1}^{N}\;{{I_{i}\left( {k + {\hat{m}}_{i}} \right)}.}}}}$The estimation of {circumflex over (m)}_(i), i=2, . . . , N, depends onthe over-sampling rate. A high over-sampling rate gives a more accuratedelay value of {circumflex over (m)}_(i). When the over-sampling rate islow, interpolation and re-sampling can be advantageously used to improvethe accuracy of {circumflex over (m)}_(i). It is noted that the termsΔs_(i)(k), n_(i)(k), and I_(i)(k) are eliminated by taking averages. Ifall of those terms have zero means, and A(k) approaches a constantnumber A, we have ΔS(k)+L(k)+I(k)→0 and A(k)→A when the number ofreceiving sensors 11, 12 and N is large, that is N→∞. This yields thefollowing expression:y(k)≈A·s(kT _(s))  Equation (8)The weak signal s(kT_(s)) is then recovered from the noisy channels byusing the multi-sensor network systems of the present invention.

Usually, a preprocessing operation is needed to exclude the outlierpackets based on the estimated signal-to-noise ratios (SNRs) and tonormalize the packets based on the signal powers before estimating thedelay factor and combining the signals. Thus, the multi-sensordemodulation device 10 provides signal fusion, automatic demodulation,modulation scheme classification, and the appropriate demodulationtechnique to effectively monitor the collected non-cooperative unknownsignals without suffering form the disadvantages, shortcomings, andlimitations of prior art techniques and devices.

This invention can be implemented in, either in hardware or software.FIG. 3 is a software programming flowchart that illustrates theoperation of software in this invention's multi-sensor signal fusionarticle of manufacture with a storage medium encoded withmachine-readable computer program code for more accurate descriptions ofmonitored signals. The software programming flowchart depicts thesoftware operations of the signal preprocessing, delay factorestimation, and signal combining processes.

Referring now to FIG. 3, when this invention is implemented withsoftware, the software operation begins with collecting signals in ameans for collecting signals and storing data represented by Block 21,where signals collected from multiple sensors are transmitted to adigital signal processing unit in the master and stored in the memoryfor processing. In Block 22, a coarse SNR estimation is conducted in ameans for coarse estimation in order to eliminate the outliers based onthe SNR threshold. In a means for sorting represented by Block 23, theSNRs are sorted from high to low, and signals with a SNR below a giventhreshold are excluded. In Block 24 a means for normalization normalizessignals above a given threshold, and in a means for signal labeling,represented by Block 25, the signals are labeled from 1 to N_(n), thatis r_(j)(k), j=1, 2, . . . , N_(n), based on the estimated values ofSNRs. Here the index j is not related to the indices of the sensors. InBlock 26 a means for correlating receives the signal with the highestSNR, r₁(k), and correlates it with r₂(k) to obtain the delay factor{circumflex over (m)}₂ in Block 27. In Block 28, a means for calculatingaverages r₁(k) and r₂ (k+{circumflex over (m)}₂), which are defined asr_(a)(k) and continuing the similar process, as shown in FIG. 3, forr₃(k), r₄(k), . . . , r_(N) (k) finishes the looping process with theBlock 26 correlating means and Block 27 delay factor resulting in acombined signal 29 fed to a signal detection and modulationclassification block 29 for estimating the modulation scheme. Many ofthe variations of the multi-sensor demodulation device also apply tothis invention's article of manufacture software embodiment.

FIG. 4 is a conceptual block diagram of another hardware implementationof the multi-sensor non-cooperative demodulation device 40 of thepresent invention that provides more detail concerning the signalpreprocessing, delay factor estimation, and signal combining aspects ofthe device with master and slave components. This embodiment provides afirst, or master, sensor 41 and an i^(th), or slave, sensor 42.

The signals are collected by sensor antennas 43 and 44, sent toAnalog-to-Digital Converters 45 and 46 and then digitized by a localclock 47 and 48 where i, i=1, 2, . . . , N, and saved in a local memorymodule 49 and 50. The master sensor 41 collects the multiple signalpackets from local memories, then estimates coarse SNRs in a means forSNR estimation 51, excludes outliers in a means for sorting 52, and thennormalizes all the signals in a means for signal fusion 53. Atransmission delay factor 54 is estimated and then the signals arecorrelated in a means for signal correlation 55. Interpolation andover-sampling will be applied if needed. The signals are shifted andcombined in a means for signal combining 56 before feeding to theautomatic modulation classification block 57. FIG. 4 only demonstratestwo sensors, one is the master and the other is the slave. The samearchitecture works for a large sensor network with massive numbers ofslaves. Parallel processing can be used for estimating the delay factorand combing signals. Multiple master sensors can be used to distributethe signal fusion process in accordance with the present invention. Manyof the variations of the multi-sensor demodulation device also apply tothis invention's master/slave sensor configurations.

Referring now to the drawings, FIGS. 5A and 5B are charts illustratingsimulation results of a single sensor and a multi-sensor signal fusionwith matched filters that demonstrate the advantages in usingmulti-sensor signal fusion in accordance with this invention. Thecomputer simulations were conducted by combining signals received from100 receiving sensors. The SNR ratio and signal length at each singlesensor is 0 dB and 512 samples, respectively. The signals are modulatedas 16 QAM with root-raised-cosine filters. The roll-off factor is 0.25and the over-sample rate is 4 samples per symbol. In order to simplifythe simulations, all signals were digitized synchronously in time andmodulation phase. The results of these computer simulations are shown inFIGS. 5A and 5B. The dots in FIG. 5A are recovered symbols at a singlesensor which are very noisy, and are not recognizable for anyconstellation pattern. By contrast, the FIG. 5B multi-sensor signalfusion dots are arranged in a much clearer constellation pattern of 16clusters. Therefore, the unknown signal is classified as QAM16modulation scheme.

Matched filters were used in the FIG. 5A and FIG. 5B simulations. FIG. 6illustrates the simulation result of multi-sensor signal fusion withoutmatched filters because in most non-cooperative communicationoperations, the structure of the matched filter is not always known sothe matched filter cannot be used in those situations. The dots in FIG.6 are the recovered symbols after multi-sensor signal fusion with nomatched filter. Although the 16 clusters in FIG. 6 are not asconcentrated as those in FIG. 5B, those skilled in the art shouldreadily recognize them and classify the unknown signal as the QAM16modulation scheme. After comparing the FIG. 5A single sensor resultswith the FIG. 5B and FIG. 6 multi-signal fusion results, it is readilyapparent that the FIG. 5A single sensor modulation scheme at SNR=0 dB isalmost impossible to discern, while the FIG. 5B and FIG. 6 multi-sensorresults quite readily allow estimating the modulation scheme, even ifthe SNR is quite low.

The multi-sensor signal fusion technique can be developed in variousimplementations and embodiments. The concept applies to both analog anddigital signals in any wired or wireless communication network withvarious architectures, to a wide frequency range, and to the channels inharsh environments.

FIG. 7 is a conceptual block diagram depicting a multi-sensornon-cooperative linear digital signal classification device 60 forclassifying linear digital signals including M-ary PSK and M-ary QAMmodulation schemes in accordance with the present invention. Thisembodiment illustrates the processing sequence of the estimations ofcenter frequency, bandwidth, SNR, and symbol rate, and gives a top-levelview of automatic modulation classification of linearly modulateddigital signals. The automated modulation classification includes, butis not limited to, analog, linear and nonlinear digital, and variousmultiple carrier signals.

This multi-sensor non-cooperative linear digital signal demodulationdevice 60 comprises a coarse modulation parameter estimation unit 62 anda fine modulation parameter estimation unit 61. The signals arecollected by sensor antennas and combined by a signal fusion means notshown in this drawing. Referring now to the coarse estimation unit 62,the fused multi-sensor signal 63 is used for coarse estimations of thecenter frequency in a means for center frequency estimation 64, coarseestimations of bandwidth in a means for bandwidth estimation 65, andcoarse SNR estimations in a means for SNR estimation 66. The signal isdown-converted and filtered in a first band-pass filter 67 based on thecoarse estimations of the center frequency and bandwidth. Then afiltered signal output 68 is provided to a means for symbol rateestimation 69 and a means for signal re-sampling 70 to the integernumber of samples per symbol. The signal re-sampling means 70 sends asampled, filtered output 71 to the fine modulation parameter estimationunit 61, which functions as a master sensor.

Referring now to the fine estimation unit 61, or master sensor, theresidual center frequency is removed from the sampled, filtered output71 and the signal is mixed and filtered once again with a second bandpass filter 72 that is tighter than the first band pass filter 67. Thetwice-filtered output signal is down sampled to the symbol rate, ifneeded, in a means for down-sampling 73 before channel estimation isperformed in a means for channel estimation 74 and before channelequalization occurs in a means for channel equalization 75. Themodulation phase offset is estimated in means for phase estimation 76and corrected in a means for phase correction 77. A maximum likelihoodalgorithm software module 78 estimates the most likely modulation schemebased on the estimated SNR and possible modulation schemes stored in amodulation schemes storage module 79. The confidence of the modulationestimation is measured in a means for estimation measurement 80 andestimation results, including modulation scheme, SNR, bandwidth, symbolrate, center frequency residual, and estimation confidence, are reportedin final estimate, represented by arrow 81 once the multi-sensor signalis obtained and combined. The automatic modulation classification doesnot depend on, and is not limited to, the signal fusion methods. Inother words, any existing or new automatic modulation classificationmethods can be used in this invention. Many of the variations of themulti-sensor demodulation device also apply to this invention'smulti-sensor non-cooperative linear digital signal demodulationembodiment.

Referring now to FIG. 8, there is depicted a flow diagram of the stepsof this invention's method for achieving increased fidelity and morereliable simulation of monitored non-cooperative signals withmulti-sensor non-cooperative demodulation comprising the steps ofreceiving non-cooperative signals, s(t), from an unknown transmissionsource in a group of sensors, each of the sensors having a samplingclock and a local memory, with the non-cooperative signals having weaksignals, a given modulation and a given demodulation; digitizing a groupof received signals with the group of sensors; providing digitizedsignals, with the digitized signals including the multiplenon-cooperative signals; and transmitting the digitized signals to asignal fusion sensor, which are represented by Block 101. The step ofproviding a coarse SNR estimation from a means for coarse estimation toextract the weak signals based on a coarse SNR threshold is representedby Block 102 and the step of sorting the digitized signals according toan SNR value below a given threshold in a means for sorting isrepresented by Block 103. The step of normalizing digitized signals withSNR above a given threshold is represented by Block 104, and the step oflabeling the high SNR digitized signals in a means for signal labelingbased on multiple estimated SNR values is represented by Block 105.

This invention's method continues with the steps of generating acombined digitized signal with a maximum SNR value, r₁(k), in a meansfor correlating, represented by Block 106; correlating the maximum SNRdigitized signals with r₂(k) to obtain a delay factor {circumflex over(m)}₂ represented by Block 107; averaging r₁(k) and r₂ (k+{circumflexover (m)}₂) in a means for calculating, represented by Block 108; andtransmitting a combined digitized signal to a means for automaticmodulation for a modulation output estimate, represented by Block 109.Block 110 represents the final steps of sending the modulation outputestimate to a means for modulation scheme classification that selects ademodulation technique by evaluating the modulation output estimate andthe given demodulation; generating a matching demodulation output in themodulation scheme classification means; sending the matchingdemodulation output to a means for signal demodulation to generate ademodulated signal; and simulating the non-cooperative signals withoutunwanted channel noise, disturbances and interference allowing a user tocovertly identify and monitor the unknown transmission source with animproved fidelity and reliability. Many of the variations of themulti-sensor demodulation device also apply to this invention's methods.

It is to be further understood that other features and modifications tothe foregoing detailed description are within the contemplation of thepresent invention, which is not limited by this detailed description.Those skilled in the art will readily appreciate that any number ofconfigurations of the present invention and numerous modifications andcombinations of materials, components, arrangements and dimensions canachieve the results described herein, without departing from the spiritand scope of this invention. Accordingly, the present invention shouldnot be limited by the foregoing description, but only by the appendedclaims.

1. A multi-sensor non-cooperative demodulation device, comprising: aplurality of sensors receives a plurality of non-cooperative signals,s(t), from an unknown transmission source, each of said sensors having asampling clock and a local memory, and said plurality of sensorsprovides a plurality of received signals, one of said plurality ofsensors being a signal fusion sensor; said plurality of non-cooperativesignals having a plurality of weak signals, a given modulation and agiven demodulation; a first one of said plurality of sensors digitizessaid plurality of received signals to provide a plurality of digitizedsignals; said plurality of digitized signals being combined in a signalfusion sensor; said signal fusion sensor extracts said plurality of weaksignals from said plurality of digitized signals and generates acombined digitized signal with a maximum signal-to-noise ratio, r₁(k),to obtain a delay factor {circumflex over (m)}₂; said combined digitizedsignal with a maximum signal-to-noise ratio, r₁(k), is sent to a meansfor automatic modulation classification for a modulation outputestimate; said automatic modulation classification means sends saidmodulation output estimate to a means for modulation schemeclassification that selects a demodulation technique by evaluating saidmodulation output estimate and said given demodulation; and saidmodulation scheme classification means sends a matching demodulationoutput to a means for signal demodulation to generate a demodulatedsignal that simulates said plurality of non-cooperative signals withoutunwanted channel noise, disturbances and interference allowing a user tocovertly identify and monitor said unknown transmission source with animproved fidelity and reliability.
 2. The multi-sensor non-cooperativedemodulation device, as recited in claim 1, further comprising a firstone of said plurality of sensors digitizes a short time durationfragment of said plurality of received signals to a plurality of Ksamples.
 3. The multi-sensor non-cooperative demodulation device, asrecited in claim 2, further comprising said plurality of sensors storingsaid plurality of K samples in a local memory, said plurality of Ksamples being time-stamped.
 4. The multi-sensor non-cooperativedemodulation device, as recited in claim 3, further comprising saidplurality of sensors being a master sensor and a plurality of slavesensors.
 5. The multi-sensor non-cooperative demodulation device, asrecited in claim 4, further comprising a means for data processinghaving a plurality of software programs and a storage medium encodedwith machine-readable computer program code.
 6. The multi-sensornon-cooperative demodulation device, as recited in claim 5, furthercomprising signal transmission between said plurality of slave sensorsand said master sensor being asynchronous in time with a plurality ofdata fragments being sent as packets.
 7. The multi-sensornon-cooperative demodulation device, as recited in claim 6, furthercomprising signal transmission between said master sensors and saidplurality of slave sensors being wireless.
 8. A method of a multi-sensornon-cooperative demodulation, comprising the steps of: receiving aplurality of non-cooperative signals, s(t), from an unknown transmissionsource in a plurality of sensors, each of said sensors having a samplingclock and a local memory, said plurality of non-cooperative signalshaving a plurality of weak signals, a given modulation and a givendemodulation; digitizing a plurality of received signals with said groupof sensors; providing a plurality of digitized signals, said pluralityof digitized signals including said plurality of non-cooperativesignals; transmitting said plurality of digitized signals to a signalfusion sensor; providing a coarse signal-to-noise (SNR) estimation froma means for coarse estimation to extract said plurality of weak signalsbased on a coarse SNR threshold; sorting said plurality of digitizedsignals according to an SNR below a given threshold in a means forsorting; normalizing a plurality of digitized signals with an SNR abovesaid given threshold to provide a plurality of high SNR digitizedsignals labeling said plurality of high SNR digitized signals in a meansfor signal labeling based on a plurality of estimated SNR values;generating a combined digitized signal with a maximum SNR value, r₁(k),in a means for correlating; correlating said maximum SNR value withr₂(k) to obtain a delay factor {circumflex over (m)}₂; averaging saidr₁(k) and r₂(k+{circumflex over (m)}₂) in a means for calculating;transmitting said combined digitized signal with said maximum SNR,r₁(k), to a means for automatic modulation for a modulation outputestimate; sending said modulation output estimate to a means formodulation scheme classification that selects a demodulation techniqueby evaluating said modulation output estimate and said givendemodulation; generating a matching demodulation output in saidmodulation scheme classification means; sending said matchingdemodulation output to a means for signal demodulation to generate ademodulated signal; and simulating said plurality of non-cooperativesignals without unwanted channel noise, disturbances and interferenceallowing a user to covertly identify and monitor said unknowntransmission source with an improved fidelity and reliability.
 9. Amethod of a multi-sensor non-cooperative demodulation, as recited inclaim 8, further comprising the step of digitizing a short time durationfragment of said plurality of received signals to a plurality of Ksamples in a first one of said plurality of sensors.
 10. A method of amulti-sensor non-cooperative demodulation, as recited in claim 9,further comprising the step of storing said plurality of K samples in alocal memory, said plurality of K samples being time-stamped.
 11. Amethod of a multi-sensor non-cooperative demodulation, as recited inclaim 10, wherein said plurality of sensors are a master sensor and aplurality of slave sensors.
 12. A method of a multi-sensornon-cooperative demodulation, as recited in claim 11, further comprisingthe step of including a means for data processing.
 13. A method of amulti-sensor non-cooperative demodulation, as recited in claim 12,further comprising the steps of: including a plurality of softwareprograms in said data processing means; and including a storage mediumencoded with machine-readable computer program code in said dataprocessing means.
 14. A method of a multi-sensor non-cooperativedemodulation, as recited in claim 13, further comprising the step ofproviding signal transmission between said plurality of slave sensorsand said master sensor that is asynchronous in time with a plurality ofdata fragments being sent as packets.